The present invention relates to measurement displays, and more particularly to a chrominance to luminance delay and gain measurement display for composite color video signals having a graphic display in rectangular coordinates.
In color television the video signal consists of a luminance, or brightness, component to which is added chrominance, or color, information which has been modulated onto a subcarrier frequency. The luminance and chrominance components of a video signal are not independent. The amplitude of the chrominance component must be correct with respect to the amplitude of the luminance component for the saturation of the color picture to be correct, and the delays of the two signals must be equal within small limits if color fringes due to misregistration are not to be apparent. Therefore to test the chrominance channel of a video device or system a signal that contains a luminance reference for the chrominance is essential. The various test signals developed for the testing of the relationship of the luminance and chrominance channels in delay and gain include a modulated pulse waveform and a bar waveform. The test signals are the linear sums of a luminance waveform and a 100% amplitude modulated subcarrier version of the luminance waveform.
A composite test pulse waveform is shown in FIGS. 1(a)-1(d) illustrating the effect of chrominance to luminance delay and gain upon the pulse waveform. As shown in FIGS. 1(a) and 1(b) when the chrominance gain exceeds the luminance gain the baseline of the envelope bulges downward, and when the luminance gain exceeds the chrominance gain the baseline of the envelope bulges upward. Where chrominance leads luminance the baseline of the envelope takes on the shape of a negative going sinusoid, while where chrominance lags luminance the baseline of the envelops takes on the shape of a positive going sinusoid as shown in FIGS. 1(c) and 1(d). The ideal situation is for the baseline of the envelope to be flat. However it is not possible from the waveforms shown in FIGS. 1(a)-1(d) to determine the exact amount of such gain or delay inequalities. For this purpose nomograms have been prepared as shown in FIG. 2. However the presence of chrominance-luminance intermodulation falsifies attempts to use it for the measurement of gain inequalities.
What is desired is a measurement display which accurately displays the chrominance to luminance delay and gain in a video signal resulting from variations ithe luminance and chrominance channels of a video device or system in a more useful form for a user.